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https://github.com/dalvarezperez/CreateFile_based_rootkit


https://github.com/dalvarezperez/CreateFile_based_rootkit

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README 

        
# Bug explaination  



**NtCreateFile** can create and access directories using names like " ." but **CreateFile** can't do it. Following the same example, it changes it to " " which is an absolutely different directory.  

It is done by KERNELBASE!_imp__RtlDosPathNameToRelativeNtPathName_U_WithStatus which "Remove any trailing spaces or dots for the last path element, assuming that it isn’t a single or double dot name" as explained here: "Types of DOS Path" section of https://googleprojectzero.blogspot.com/2016/02/  

See the following screenshot taken when accessing to " ." using **explorer.exe**.  



![alt text](screenshots/screenshot1.png "Accessing to ' .' from explorer.exe")



# Implications  



1. You can hide malware from antivirus agents which uses CreateFile to access files and directories.  

2. You can also hide malware from users who uses programs like **explorer.exe** and **cmd.exe** which, finally, relies on CreateFile.



# Disclosure  



Microsoft will not fix this issue because of the following reason:  

"This is a known portion of the file structure and is detailed online. Beyond that, an attacker would already need to have compromised a machine to make use of this".  



**I decided to publish the code.**  



**UPDATE:** I asked to Microsoft for the online documentation and they, kindly, reply to me with this link (https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file?redirectedfrom=MSDN) and referring to this phrase: "Do not end a file or directory name with a space or a period. Although the underlying file system may support such names, the Windows shell and user interface does not."  



# PoC  



[PoC file](./PoC.c)  

[Mini DDK dependency](./miniddk.h)  

  

**Note***: If you are testing the PoC and wants to remove the resulting "C:\ .\" directory, a simple way to do it is by using the GIT console:  



# Debugging session  



#### 1. Kernel32!CreateFileW calls to KERNELBASE!CreateFileInternal  

771de463 8364240c00      and     dword ptr [esp+0Ch],0  

771de468 8b4514          mov     eax,dword ptr [ebp+14h]  

771de46b 8b550c          mov     edx,dword ptr [ebp+0Ch]  

771de46e 8b4d08          mov     ecx,dword ptr [ebp+8]      ; u"C:\ .\my_hidden_malware.exe"  

771de471 89442410        mov     dword ptr [esp+10h],eax  

771de475 8b4520          mov     eax,dword ptr [ebp+20h]  

771de478 6a00            push    0  

771de47a 89442418        mov     dword ptr [esp+18h],eax  

771de47e 8d442404        lea     eax,[esp+4]  

771de482 50              push    eax  

771de483 ff7518          push    dword ptr [ebp+18h]  

771de486 ff7510          push    dword ptr [ebp+10h]  

771de489 e812000000      call    KERNELBASE!CreateFileInternal (771de4a0)  

  

  

#### 2. Debugging session in KERNELBASE!CreateFileInternal  

KERNELBASE!CreateFileInternal:  

771de4a0 8bff            mov     edi,edi  

771de4a2 55              push    ebp  

771de4a3 8bec            mov     ebp,esp  

771de4a5 83e4f8          and     esp,0FFFFFFF8h  

771de4a8 81ec84000000    sub     esp,84h  

771de4ae a1307b2a77      mov     eax,dword ptr [KERNELBASE!__security_cookie (772a7b30)]  

771de4b3 33c4            xor     eax,esp  

771de4b5 89842480000000  mov     dword ptr [esp+80h],eax  

771de4bc 53              push    ebx  

771de4bd 56              push    esi  

771de4be 8b7510          mov     esi,dword ptr [ebp+10h]  

771de4c1 8bd9            mov     ebx,ecx                 ; u"C:\ .\my_hidden_malware.exe"  

  

  

#### 3. RtlInitUnicodeStringEx works well putting u"C:\ .\my_hidden_malware.exe" into [esp+34]    

771de4fe c744241401000000 mov     dword ptr [esp+14h],1  

771de506 53              push    ebx                    ; Source  

771de507 8d442434        lea     eax,[esp+34h]  

771de50b 50              push    eax                    ; <----- Destination  

771de50c ff1570b12a77    call    dword ptr [KERNELBASE!_imp__RtlInitUnicodeStringEx  



0:000:x86> du poi(esp+34)  

0040422c  "C:\ .\my_hidden_malware.exe"  

  

  

#### 4. Then, the string is passed to KERNELBASE!_imp__RtlDosPathNameToRelativeNtPathName_U_WithStatus  

771de549 50              push    eax  

771de54a 6a00            push    0  

771de54c 8d442438        lea     eax,[esp+38h]  

771de550 50              push    eax  

**771de551 53              push    ebx                   ; "C:\ .\my_hidden_malware.exe"**  

**771de552 ff1538b92a77    call    dword ptr [KERNELBASE!_imp__RtlDosPathNameToRelativeNtPathName_U_WithStatus (772ab938)] ds:002b:772ab938={ntdll_77d00000!RtlDosPathNameToRelativeNtPathName_U_WithStatus (77d412f0)}**  



  



#### 5. And then, the vulnerability happens.  

**771de552 ff1538b92a77    call    dword ptr [KERNELBASE!_imp__RtlDosPathNameToRelativeNtPathName_U_WithStatus (772ab938)]**  

771de558 85c0            test    eax,eax  

771de55a 0f88f61e0300    js      KERNELBASE!CreateFileInternal+0x31fb6 (77210456)  

**771de560 8b442434        mov     eax,dword ptr [esp+34h] ; "\??\C:\ \my_hidden_malware.exe"**